1. Field of the Invention
The present invention relates to an ink jet recording apparatus adapted for use in a printer, a facsimile, a word processor, a copying machine or the like, and more particularly to a method for detecting the temperature characteristics of an ink jet recording head and judging the discharge state thereof.
2. Related Background Art
Recording apparatus for recording on a recording medium such as paper or a sheet for overhead projector have been commercialized in the form employing a recording head of various recording methods. Such recording head is known, for example, in the wire dot method, the thermal method, the thermal transfer method or the ink jet method. Particularly the ink jet method is attracting attention as a quiet recording method of a low running cost, since the ink is directly discharged onto the recording medium.
In such ink jet recording apparatus, an ink tank containing ink is connected to the recording head through an ink supply pipe, and the ink is supplied from such ink tank. Said ink tank may be formed as an ink cartridge which is separate from the recording head and is replaceably mounted in the recording apparatus, or as an integral unit with the recording head, which is integrally replaceably mounted in the recording apparatus.
In such ink jet recording apparatus, if the ink supply is interrupted because of the exhaustion of ink, the ink discharge becomes no longer possible so that the recording ability is lost. In order to avoid such situation, there has been commercialized the recording apparatus with a function of detecting the remaining ink amount, thus generating an alarm signal or requesting the replacement of the ink tank, according to the amount of consumption of ink.
For detecting the remaining ink amount, there has been proposed a method of counting the pulse signals supplied for ink discharge and thereby calculating the amount of ink consumption, a method of inspecting the change in the resistance of ink itself or of a member holding the ink, a method of detecting the weight change of the ink tank, or a method of forming a transparent area in an ink path in the ink tank or in the recording head and inspecting the presence or absence of ink in said ink path by the observation of the user or by a photosensor.
In the above-mentioned method utilizing the count of the ink discharge pulse signals, the remaining ink amount is detected by calculating the ink amount used in recording, from the product of the number of applied pulses and the amount of discharge per ink droplet discharged by a pulse.
Also the method of remaining amount detection by inspecting the resistance of ink etc. utilizes a fact that ordinary ink has a certain specific resistance due to the presence of water and other conductive substances therein, measures the resistance of the ink or the member holding the ink by means of a pair of electrodes provided for example in the ink tank, and detects the remaining ink amount based on a fact that the resistance between said electrodes is correlated with the remaining ink amount.
Also the method utilizing the weight change of the ink tank relies on the change of force applied to a spring provided in a member for mounting the ink tank, resulting from ink consumption, and detects the remaining ink amount by activating an electrical contact by the deformation of said spring.
However, such conventional methods as explained above have been associated with the following drawbacks.
The limit remaining amount, at which the recording operation becomes impossible, detected by the above-mentioned methods, is influenced for example by the unit-to-unit fluctuation of the recording head in manufacture, and is not highly reliable, so that the recording operation may be disabled immediately after the warning for such limit remaining amount or may still be properly conducted even after such warning. According to the experiments of the present inventors, such drawbacks is particularly conspicuous in case ink is held in the ink tank by means of an ink holding member such as sponge.
Besides the amount of ink droplet discharge per pulse is influenced not only by the unit-to-unit fluctuation of the recording head but also by the ambient temperature, so that the exact calculation of the amount of ink consumption is difficult. Furthermore, the detection by visual inspection or by photosensor has been unable to provide sufficient accuracy.
Furthermore, the configuration becomes complex by the presence of the detection members such as the spring or the photosensor, or the presence of the transparent area, for the detection of the remaining ink amount.
Furthermore, the above-mentioned conventional methods, though being capable of detecting the disabled recording state resulting from the interruption of ink supply caused by the ink exhaustion, are unable to detect the disabled recording state that may occur before the complete exhaustion of ink. Such disabled recording state before the ink exhaustion may be caused, for example, by bubble formation, by air intrusion, in the ink path between the ink tank and the recording head, or by interruption of ink supply due to generation or growth of a remaining bubble in a recording head designed to generate a bubble for ink discharge, or by destruction of meniscus at the ink discharge opening due to vibration applied to the recording apparatus or the recording head, thereby causing the liquid to flow into the nozzle of the recording head from said ink discharge opening.